The present invention relates to a method for detecting an arc in an electrical circuit, to a detection circuit implying the said method and to a switching device comprising such a circuit.
In the description herein below, the references between square brackets ([ ]) refer to the list of references presented at the end of the text.
In electrical circuits, certain faults may lead to the generation of undesirable electrical arcs. Two main types of faults are differentiated.
The first type of fault occurs when a gap is created between two elements of the circuit in the path of the current. At low voltage, no current flows; however, with a voltage that depends in particular on the width of the spacing, an arc is established in the spacing and the current flows. This is then referred to as a fault of the series arc type. In the case of an alternating current, an arc is established upon each half-alternation.
The second type of fault occurs when a spurious conductor tends to short-circuit the current source of the electrical circuit. Here again, a gap subsists between a main conductor and the spurious conductor. With a low voltage, no current flows between the two conductors, but when the voltage increases, an arc is established in the gap and the current flows forming a short-circuit. A similar phenomenon can occur when a conducting liquid simultaneously wets two conductors with different potentials. This is then referred to as a fault of the parallel arc type.
Local heating takes place which can be dissipated if the arc is not frequent, but which may lead to destructive consequences if it occurs frequently or in a repeated fashion. Moreover, the power supply for the circuit is weakened. Furthermore, the short-circuit current can also heat the spurious conductor and cause a fire.
A protection device for an electrical circuit has already been provided comprising a device for detecting an electrical arc. The document EP 1 845 599 A1 [1] shows one example of such devices. The detection is based on the measurement of the power supply current and voltage of the electrical circuit and on the digital analysis of these signals. Several detection units compare the values of the signals, of their derivative and of their integration to thresholds in order to supply signals for assisting the decision, each detection unit being adapted to one particular type of electrical arc. Decision means receive the signals for assisting the decision in order to supply a control signal for opening the electrical circuit and rendering it safe.
In another document [2], a circuit for detecting an electrical arc is applied to the semiconductor power control. In this document, the use is also provided of decision means receiving the results from several detection units. In one of them, a detection by interpolation of the input signal taken from between the current and the voltage is provided. The signal is under-sampled then interpolated by a polynomial. Subsequently, the interpolation is compared with the original signal and a warning is generated if the difference exceeds a predetermined threshold.
Even though this method of detection works well, it requires many complex calculations to be carried out, which accordingly requires a high-performance, and hence costly, detection circuit.
The invention aims to provide a method for detecting an electrical arc that is simple to implement, efficient and does not require significant processing means.